This invention relates generally to the field of chemical processing of corrosive fluids, and more particularly to an improved sight glass construction forming part of a vacuum-powered sampling means used to check the progress and condition of a reacting mass of material within a reaction vessel. Reference is made to U.S. Pat. No. 4,594,903 dated June 17, 1986 which discloses a system for accomplishing periodic sampling which includes a transparent sight glass through which a portion of a sample drawn from a reaction vessel may be viewed.
The typical sight glass, while adequately resistant to the effects of corrosive fluids is also quite fragile, and should breakage occur, the resultant leakage can result in serious damage. Further leakage can often occur as a result of failure of a check valve which normally prevents the flow of corrosive fluid therepast to result in contamination of the vacuum system used to withdraw fluid from the vessel.